1. Field
The present invention relates to electrical connectors for cables. More particularly, the invention pertains to right angle connectors for cables containing twisted pair conductors, such as RJ-45 data connectors.
2. Background
Transmission of electronic data between computational systems and/or nodes of a communication network over electrical cables is well known. Such cables often employ a multi-channel end plug similar in configuration to a rectangular telephone plug. The plug is plugged into a corresponding jack on a piece of equipment to complete a communication link.
One such widely used plug is an “RJ-45” plug.
RJ-45 plugs are commonly used at the ends of Category 5 cables having eight wires or channels comprised of four “twisted pairs.” A twisted pair is two wires twisted around each other (like a double helix) over their length. This is an advantageous way to transmit signals when the two wires carry opposite or complementary signals. This typically occurs when one wire is the transmit wire and the other wire is the return wire or when a signal is transmitted as a complementary signal on two wires. The twisting of the two wires about each other causes the electromagnetic fields generated by the two signals to cancel each other out outside of the two wires. This helps reduce or eliminate electromagnetic interference (EMI) from external sources as well as crosstalk between neighboring twisted pairs.
Specifications have been developed for twisted pair cables and the associated connectors in order to provide standardization and minimum quality requirements for such links. One such standard is what is commonly termed “Category 5” or “Cat 5”. The specification for Category 5 cables and connectors is defined in ANSI/TIA/EIA-568-A, with clarification in TSB-95. These documents specify performance characteristics and test requirements for frequencies of up to 100 MHz. Most Cat 5 cables in use today are unshielded, relying on the twisted pair design for noise rejection.
Cat 5 cabling is commonly employed to carry many different types of data signals, including basic voice services, token ring, ATM (at up to 155 Mbit/s, over short distances). Cat 5 cabling is most commonly used for 100 Mbit/s networks, such as 100BASE-TX Ethernet. Cat 5 cables include a plurality of insulated twisted pairs housed in a single insulated cable jacket. The Cat 5 specification require three twists per inch of 24 gauge (AWG) copper wires.
The Cat 5 specification has been superseded by the Category 5e specification for structured cabling for computer networks such as Ethernet. Category 5e cabling is an enhanced version of Cat 5 that adds specifications for far end crosstalk. It was formally defined in 2001 as the TIA/EIA-568-B standard. The tighter specifications associated with Category 5e cables make it an excellent choice for use in 1000BASE-T network applications. Cat 5e cable and connector performance characteristics and test methods are defined in TIA/EIA-568-B.2-2001.
RJ-45 plugs are commonly used to terminate Cat 5e cables. In an RJ-45 connector, the ends of the twisted pair wires of the cable are untwisted, laid out (usually in a plane), and electrically connected to contacts in the plug body that will mate to corresponding contacts in a mating RJ-45 jack on a piece of equipment, panel or bulkhead, when the plug and the jack are connected. If the wires of the twisted pairs are unraveled (i.e., untwisted) over even a very short distance at the end of a cable for purposes of connecting the wires to the contacts in the terminating plug, the cable may not meet the requirements of the Category 5e specification. Thus, the wires still should be maintained in the twisted pair configuration up to a point as close as possible to the front end of the plug body before being untwisted and laid out in the aforementioned plane in order to assure that the cable and connector stay within the Category 5e specification.
In applications where the space in front of an RJ-45 jack to which a Category 5e cable with an RJ-45 plug is to be connected is limited, it may be necessary or desirable for the cable to make a sharp bend in as short a distance as possible out of the back of the RJ-45 connector. Generally, the amount by which the cable can be bent adjacent the connector is limited by the properties of the cable and any overmold and/or strain relief placed over the cable adjacent the connector
When a twisted pair is bent to form a curve, such as in a right angle connector, the two wires forming the twisted pair have a tendency to separate and/or untwist from each other. The shorter the radius of the curve, the more the wires tend to separate and untwist from each other. Furthermore, the cable and its connector are vulnerable to separation or electrical discontinuity in one or more wires due to the sharp flex at the point of entry of the cable into the connector body. Too sharp of a bend in the wires of a twisted pair also can adversely affect signal quality in the cable.
These phenomena make it difficult to manufacture a twisted pair cable with a right angle connector with a short radius bend. The radius of the arc of the twisted pairs must be relatively long to avoid untwisting or the cable may not meet the Category 5e specification.